DPP-IV is one kind of serine protease hydrolyzing a dipeptide Xaa-Pro or Xaa-Ala (Xaa may be any amino acid) specifically from the N-end of a polypeptide chain. The role of DPP-IV (also called CD26) in vivo and the relationship of this enzyme with diseases are not completely elucidated, but there are many reports thereon. In particular, attention is paid recently to the role of DPP-IV as an enzyme participating in the inactivation of glucagon-like peptide 1 (abbreviated hereinafter to GLP-1).
GLP-1 is a peptide hormone which without inducing insulin secretion by itself, has an action of increasing insulin secretion induced by glucose. Accordingly, its enhancement of insulin secretion depending on blood glucose level can be expected with less possibility of hypoglycemia. Further, there is also a report suggesting that GLP-1 has an appetite suppressing action. However, GLP-1 is rapidly cleaved by DPP-IV, so GLP-1 itself is hardly applicable as medicine. Accordingly, peptide analogues of GLP-1 have been examined, but any of such analogues are injections, but are not preparations for oral administration.
Under these circumstances, inhibition of the cleavage enzyme DPP-IV was anticipated in order to prevent the degradation of GLP-1 thereby enhancing the activity of GLP-1. This involves orally administering a DPP-IV inhibitor thereby keeping the concentration of GLP-1 intact in vivo to prevent and treat diabetes and the like, particularly type 2 diabetes, by the action of GLP-1. Such treatment method is also expected to have an effect of preventing or treating other diseases induced or developed by impaired glucose tolerance, for example, hyperglycemia (postprandial hyperglycemia), hyperinsulinemia, diabetic complications (renal diseases, neuropathy and the like), abnormal lipid metabolism, obesity and the like. Further, its effect on prevention or treatment of diseases expected to be ameliorated by enhancing the inhibition of food intake of GLP-1, for example, bulimia, obesity and the like can also be expected.
On the other hand, the reported action of DPP-IV further includes cleavage of neuropeptides, activation of T cells, adhesion of metastatic tumor cells to endothelium, and invasion of HIV virus into lymphocytes. It is found with respect to DPP-IV and known that the positiveness of DPP-IV is increased in peripheral blood T cells from patients with rheumatism and the activity of DPP-IV is high in urine from patients with nephritis. Accordingly, a substance inhibiting DPP-IV is expected to have an effect of preventing or treating autoimmune diseases (for example, arthritis, rheumatoid arthritis), osteoporosis, acquired immune deficiency syndrome (AIDS), rejection of transplanted organs and tissues, and the like.
Patent applications relating to DPP-IV inhibitors have also been already filed. WO02/51836, WO01/96295, US20020193390, U.S. Pat. No. 6,011,155 and Japanese Patent Application National Publication No. 9-509921 disclose 2-cyanopyrrolidine derivatives, and WO97/40832 discloses aminoacyl thiazolidide derivatives. In addition to the compound group described above, Annual Report in Medicinal Chemistry, Vol. 36, pp. 191-200 (2001) reports peptide derivatives such as aminoacyl pyrrolidide derivative, dipeptide phosphonate derivative, dipeptide borate derivative, tetrahydroisoquinoline derivative and cyclic peptide derivative, and non-peptide derivatives such as N-phenylphthalimide derivative, N-phenylhomophthalimide derivative and isoquinoline derivative.